Some memories have a destructive type of access to the memory in the form of a fuse-link. Programmable read-only-memories (PROM) are typical of such memories. Once data is written into the memory the programmer has the capability of disabling access by destroying the fuse-link thereby preventing modification of that data. When, however because of packaging density, a floating-gate PROM or EPROM array is considered, the use of a fuse-link is becoming more difficult to achieve.
With the advent of semiconductor memories being used in credit or security cards it is important to disable the input to at least a portion of the memory so that secret identifying codes contained within that portion of the memory are not modified or read by an unauthorized person who has obtained possession of the identification or credit card. Wider use is being made of memories in such cards to increase the range of uses and versatility of the cards. As an example, a memory can be placed on the same semiconductor chip as a microprocessor, wherein the semiconductor chip is embedded or enclosed within the card and is activated upon each use of the card.
Accordingly, it is an object of the present invention to provide an improved means and method for disabling access to a memory on a semiconductor chip once the chip is removed from the wafer from which it was formed.
Another object of the present invention is to provide a means and method for disabling access to a portion of a semiconductor memory and at the same time to minimize the possibility of contamination affecting the active circuitry on the semiconductor chip.
Yet another object of the present invention is to provide access lines to a portion of a memory on a semiconductor chip which are severed when the semiconductor chip is separated from the wafer from which it was made.